1. Field of the Invention
The present invention relates to a window opening and closing apparatus using a motor drive, and more particularly to a window opening and closing apparatus that is capable of detecting a jamming object during the opening and closing operations.
2. Description of Related Art
A representative technique among those known for opening and closing a window with a motor is the so-called "power windows" where a side window of a vehicle is opened and closed with a motor. When automatically opening or closing a window by motor drive, it becomes necessary to perform a control operation, such as for stopping the opening or closing operation, when an object is jammed between the moving window and the window frame. This is done to prevent damage, either to the object itself or to the window, or a mechanism for opening or closing the window.
This sort of technique for detecting the jamming of an object is disclosed in Japanese Patent Laid-Open Publication No. Hei 5-95694. In this technique, pulses proportional to the rotational speed of the motor are generated and the jamming of an object is detected from a change in the period of the pulses. Namely, when an object is jammed, the load on the motor increases so that its rotational speed decreases, and jamming is detected through this decrease in rotational speed.
However, in an apparatus for opening and closing a window installed in a door, such as the side window of a vehicle, a decrease in the rotational speed of the motor may be caused by factors other than a jammed object. These other factors could even include the impact caused by normal opening and closing of the door. Furthermore, if the window is provided in a vehicle door, vibrations of the vehicle body due to the characteristics of the road surface on which the vehicle is traveling, especially the irregularities in the road surface, can also become the above-mentioned disturbances. When judging the jamming of an object from the rotational speed of the motor, as in the above-mentioned apparatus of the prior art, a problem exists in that a change in the rotational speed of the motor caused by the factors mentioned above will also be judged to be due to a jammed object.
As a specific example, when the door is opened or closed during the opening or closing of the window glass in a vehicle having power windows, the change in motor rotational speed accompanying the door opening or closing operation is incorrectly judged to be due to a jammed object jam. Furthermore, if the opening or closing operation of the window is performed when vehicle body vibrations are large due to the road surface, such as the vibrations that are caused by traveling over a rough road, the change in motor rotational speed due to vehicle body vibrations is incorrectly judged to be due to a jammed object.